The present invention generally relates to memory arrays of storage cells, and more particularly to a memory storage device with a heating element.
Magnetic Random Access Memory (MRAM) technology utilizes storage cells, for example, magnetic tunnel junctions (MTJs), which generally each have at least two magnetic regions or layers with an electrically insulating barrier layer between them. The data storage mechanism relies on the relative orientation of the magnetization of the two layers, and on the ability to discern this orientation through electrodes attached to these layers. For background, reference is made to U.S. Pat. Nos. 5,650,958 and 5,640,343 issued to Gallagher et al. on Jul. 22, 1997 and Jun. 17, 1997, respectively, which are incorporated herein by reference.
Typically, each storage cell includes a magnetically changeable (reversible) or xe2x80x9cfreexe2x80x9d region and a proximate magnetically referenced xe2x80x9cfixedxe2x80x9d region arranged into a MTJ. A storage cell can be written by reversing the free region magnetization using applied bi-directional electrical and resultant magnetic stimuli via its respective bit line and word line. The storage cell can later be read by measuring the resultant tunneling resistance between the bit line and word line, which assumes one of two values depending on the relative orientation of the magnetization of the free region with respect to the fixed region.
MRAM arrays typically include an array of data storage cells respectively positioned at intersections of word lines and bit lines. When writing storage cells, it is desirable to write only selected storage cells in the array, without affecting other non-selected cells. However, the magnetic fields generated from the bit and word line during writing can disturb the magnetization state of adjacent non-selected cells, thereby reducing reliability of the array. In addition, the magnetic state of a cell can be affected by the magnetization state of adjacent cells, especially in a dense array.
Accordingly, a need exists for improving the write selectivity of memory storage cells within a memory array.
The present invention provides techniques for increasing the write selectivity of memory storage cells and reducing the types of errors described above.
In one aspect of the invention, the invention provides a memory storage device. The storage device includes a storage cell having a changeable magnetic region. The changeable magnetic region includes a material having a magnetization state that is responsive to a change in temperature. The memory storage device also includes a heating element. The heating element is proximate to the storage cell for selectively changing the temperature of the changeable magnetic region of said storage cell.
In a preferred embodiment, the storage cell of the memory storage device includes a magnetic tunnel junction, and the changeable magnetic region is a reversible magnetic region having a magnetization state which can be reversed by applying thereto a selected magnetic field. The reversible magnetic region includes a material having a magnetization state that is responsive to a change in the temperature thereof.
Preferably, the magnetic tunnel junction further includes at least one fixed magnetic region having a magnetization state which cannot be changed or reversed by applying the selected magnetic field to the fixed magnetic region.
According to a preferred embodiment of the invention, selective heating is applied to the storage cell by passing an electric current through the heating element. The memory storage device can further include an electrically conductive terminal that is capable of receiving the electric current passing through the heating element.
As will be understood, it may be desirable to maintain the aforesaid reversible magnetic region at the compensation temperature to maintain stored data in the storage cell.
In another aspect of the invention, a memory array is provided. The memory array includes two or more memory storage devices. At least one of the memory storage devices includes a storage cell having a bit line and word line associated therewith. The storage cell includes a changeable magnetic region that includes a material having a magnetization state that is responsive to a change in temperature thereof. The memory storage device also includes a heating element proximate to the storage cell for selectively changing the temperature of said changeable magnetic region of said storage cell.
In another aspect of the invention, an integrated circuit is provided. The integrated circuit includes at least one memory storage device as set forth above and described further herein.